Interview with John Paul Wild

Begin Tape 90A

Sullivan

We’ve been looking at the original colored charts that you made up, and you were just telling me about how exciting some of –

Wild

Oh, when they actually occurred, [Oh, that is a pen one has set up] one was waiting for long periods and nothing happened, and then these things rose out of the, on the A scan of the cathode ray tube. It was tremendous excitement and whoever was observing would try and turn on the camera as quickly as possible and shout or scream to get the other one on to come and have a look at what was going on.

Sullivan

Sometimes you did miss the beginning, though –

Wild

That’s right. Invariably we’d miss the beginning. Except of course, when we learned after a while that it was a Type III burst, which were very short. They only lasted about 10 seconds and getting them was very important. But we soon learned that they tended to come in groups. So we’d keep the camera on for, oh possibly, if we missed part of the first, we’d get all of the second or third.

Sullivan

Now this thing was absolutely unique at this time, right? In fact, is it true that the next one wasn’t built until the mid or late fifties when Alan Maxwell’s –

Wild

Right. Maxwell was really –

Sullivan

Well, besides your second one.

Wild

1956. I spent the first part of 1956 with Alan Maxwell at Harvard.

Sullivan

I see. Well, we’ll talk about that a bit later on. So you had no competition exactly.

Wild

No, no competition.

Sullivan

But, tell me now about these three types. You said that they were clear cut as far as very little things, very few in-between cases or maybe none at all. What did you make of that? What did you think was going on?

Wild

Taking them in turn, well, not in the right order, but typically you start with the Type II bursts. There had been one example recorded on single frequencies by – I’m trying to think, Payne-Scott, Yabsley and Bolton.

Sullivan

Right. I think that’s correct.

Wild

And this was one unique example in which there seemed to be a drift from, a very slow drift from high frequency. Payne-Scott had followed these observations up and found no other cases, and she concluded that it was an accident. But, when that first one came, it led to a better dimension, there was a suggestion, I think it came from Pawsey, that it was perhaps due to an output within the disturbance at 1,000 kilometers per second or 800 kilometers a second.

Sullivan

The idea of different frequencies originating in different electron densities was pretty straight-forward?

Wild

Not so straight-forward. That really came out of the work, as far as we were concerned, of D.F. Martyn, and out of the quiet sun work. This was a piece of original work by Martyn. It turned out in later years that at a similar time, Ginzburg, in the Soviet Union, had come to the same conclusion and published it. A somewhat similar time.

Sullivan

But you didn’t have that translation?

Wild

No, as far as we were concerned, it was, we only knew of Martyn’s work. And so this, as we found that this was, in fact, a regularly occurring phenomenon, we found more and more evidence to favor that hypothesis. And of course, the ultimate evidence really came with the Dapto work when harmonics came along, and it had to be a resonant frequency. And the plasma frequency was the only thing that –so that was the thing that nailed the plasma hypothesis was the harmonics.

Sullivan

Well, what had it been before that? What else were you considering?

Wild

There were various theories for frequency drifts; one was a sort of great big concentration somewhere in the solar atmosphere, a concentration of electron density like a bubble that would gradually burst, as it were, a concentration which spread itself. When it came to Type III bursts, we advanced the hypothesis, not immediately. We mainly pointed out that, let me start again. There was a hypothesis by Jaeger and Westfold that, to explain the Type III bursts as different time delays as due to group retardation, and this is looked into in the third of my papers. Now, by a very systematic quantitative argument, we were able to show that this was wrong; this was completely incompatible, from a very general point of view.

Sullivan

And this was in the third paper?

Wild

This is the third paper.

Sullivan

The source cannot be fixed. What was the key part of that argument?

Wild

The key part of the argument was a subtle one; it virtually measures the curvature, this graph –

Sullivan

Figure 6?

Wild

Right. It depicts the curvature of the burst on the time-frequency plane. And what is plotted here is the time interval, the upper part of the frequency range versus the time interval on the lower part of the frequency range, so that a straight line burst, a linear burst, would fall on a 45° line. Now the Jaeger/Westfold hypothesis said that it had to fall in the shaded portion, and not one example in fact did. It fell up here. On the other hand though, the whole thing was entirely consistent with the idea of a source which moved outwards at constant velocity. And later, we didn’t push this fact, but many said it was consistent with it. Later on, when further evidence came along at the Dapto, and then we really pushed that hypothesis. We said this looks like the real thing, and met very great opposition because no one had heard of any particles from the sun which at such high-speed ejections at one-third the velocity of light. I remember that I think at the first IAU Conference I went to, in Dublin in 1955, I can remember walking along with the great man, Alfvén, him saying, “You’re wrong, you know,” and I said, “Well, let’s have a bet on it then.” I can’t remember what the bet was.

Sullivan

Or, if you ever collected? [laughing] So people were willing to accept this slow drift, 500 kilometers a second or something like that, but not the very high speeds?

Wild

Yes.

Sullivan

Oh, what was the other question that came to mind? When you were figuring out these velocities, were you just taking standard models of the electron density versus height?

Wild

Yes, indeed. By this time, there were fairly trustworthy models of the electron densities; the solar corona, and due to the work of D.F. Martyn and also, we didn’t know it at the time but in Russia by Ginzburg, the notion of different frequencies coming from different levels according to the plasma frequency had emerged. So, this is how we got our velocities, by combining these two facets.

Sullivan

But the actual models that you used were they Smerd’s perhaps?

Wild

What the actual models really were, were the models used by Steve Smerd as well. The model was really the, known as the Baumbach-Allen –

Sullivan

Ah, yes.

Wild

-- model which came from eclipse data, and what Steve Smerd’s big contribution was to work out the radiation from the quiet sun.

Sullivan

Okay. We’ve discussed the Type III, the Type II slow drift, but you haven’t mentioned anything about the correlation with flares. Could you tell me what sort of cooperation you had in these early days between optical and radio, and so forth, also?

Wild

Yes, well the solar, the international solar community is a very closely-knit cooperative one. We didn’t know very much about flares at that time. In fact, the flare as a solar phenomenon is almost entirely a post-war thing. If you look in early pre-war books, there probably, if there was anyone by (?) the flare hardly gets mentioned. Since the war, it’s become the main phenomenon really on that scale, the main phenomenon of solar activity.

Sullivan

Why was it missed? Because people weren’t looking at H-alpha perhaps?

Wild

I don’t really know why it was missed. Probably because people weren’t taking so many routine frequent observations. That is, taking pictures every second or so. (?) there was a lot of prominence across recording (?) or (?) or whatever they were.

Sullivan

But you’re right, the expense of a monitoring program, is a standard now; it would have been very great then.

Wild

Yes, but it was a very early result. Of course, the solar flare was, chromospheric reactions, right from the very word go when they were first observed in the 19th century. The suspicion of their correlation with the aurora magnetic storms. And of course, what the Type II burst has done is to establish almost beyond a doubt that the Type II burst is itself the agency which conveys the, which causes the aurora magnetic storms and links the flares with the (?)

Sullivan

Right, getting here a day or two –

Wild

And eventually we identified the phenomenon of the Type II burst as a shock wave.

Sullivan

But that comes a little bit later.

Wild

That comes a bit later, yes.

Sullivan

But now what about the correlation with the flares? Where were you getting your optical information from?

Wild

I can’t remember, this is an internationally available paper.

Sullivan

So it wasn’t any local optical astronomer; it was just these standard reports of solar activity?

Wild

Yes

Sullivan

Well, for instance, I know that C.W. Allen took some interest.

Wild

C.W. Allen did, indeed.

Sullivan

But perhaps not directly with you.

Wild

Yes, we had a lot to do with C.W. Allen. He, himself, made a very valuable series of single-frequency observations, 200 megahertz, I suppose, and did a lot of good work in helping to classify the various types of phenomenon that you could recognize on single frequency. But I don’t think in those days that Mt. Stromlo was really doing any solar work. There was a certain amount of work done at that time: observation of flares, by John Jefferies’ group, Marie McCabe from the roof of the laboratory at Sydney University. Oh, there was a fair amount of optical flare, but there was no problem of getting sufficient material.

Sullivan

But you did not develop an actual collaboration, collaborative program with them? That, say we’ll be observing next week, will you guys observe next week, or something like this?

Wild

Not really. They monitored the sun at that time, which is all we were asking for. Later on, when we were at Culgoora – I think Joe (Benetti?) himself would have been quite interested to develop a program on flares, optical flares and working closely with us, but his own collaborators were not interested in that sort of thing. There’s never been a very close, apart from a social one, there’s never been a very close sort of collaboration between the optical and the radio part.

Sullivan

Let me ask a more general question. Obviously, you were becoming educated about the sun, and perhaps even astronomy more generally – was this all just a matter of going to the library and reading books yourself? The transformation from a radio physicist to an astronomer?

Wild

Oh, I’d be just reading bits and pieces here and there, going to astronomical meetings, and talking to astronomers. Things just rubbed off. There was no systematic attempt, in my case, at least in self-education of astronomy.

Sullivan

Were there ever any, for instance, series of lectures organized in the department?

Wild

In Sydney?

Sullivan

Right, where people would bone up on different areas and give a lecture or something?

Wild

No, not really. The usual scientific colloquia people would give. I think, people like Steve Smerd occasionally would give some educational talks, but there was nothing systematic.

Sullivan

Well, along this same line, if in the early fifties someone asked you what do you do? How did you answer them? How you describe your –

Wild

I’d probably say I was a physicist. It would have been misleading and pretentious to call oneself an astronomer at that time. I think the word “radio astronomy” came in just about 1950, ‘51, or something like that.

Sullivan

Now you mentioned international meetings or astronomical meetings. When, in fact, was the first time you went to an astronomical meeting?

Wild

I went to the Dublin one in 1955.

Sullivan

There were no previous ones in Australia here?

Wild

Oh, well, the biggest, it was sort of an international event in Australia, was the URSI meeting that was held in 1951.

Sullivan

52. I think it was.

Wild

I think that was the first big international conference for the scientific unions of any kind held in Australia.

Sullivan

Did you present results at that meeting?

Wild

Yes, yes, indeed. In fact, it was really the (?) results of the (?).

Sullivan

And this probably afforded the first opportunity to meet some other people. Can you remember anyone?

Wild

Well, yes. The leader, the chairman was Appleton at the time, and there were many others who are in that photograph.

Sullivan

Oh, that’s right.

Wild

That is taken at the time of URSI. There’s — [looking at photo]

Sullivan

Mueller, Steinberg, Hagen.

Wild

Right. Doc Ewen.

Sullivan

Oh, yes.

Wild

Hanbury Brown who was from the UK.

Sullivan

That’s right, at that time.

Wild

And Laffineur, M. Laffineur from France.

Sullivan

Now I’m wondering, did you profit at all from this interaction with them or was it mainly?

Wild

Oh, very much. It was very exciting, first chance of meeting people from other countries, and it was very stimulating. They came round, I remember at that time, we’d just set up Dapto field station and they all came to visit us, including Appleton, his gray striped trousers and everything; and he gave us very great encouragement, and said all good things.

Sullivan

Okay. Going back to the fourth paper now, is the only one that we haven’t discussed, I believe. And that has to do with the “enhanced radiation,” as you call it. Could you tell me about it?

Wild

Yes, it’s become (?) noise storms or Type I storms. That is, continues really to be, the hardest to interpret, but I’m rather out of touch with the subject in the last few years; I’m not sure what advances have been made. But it’s believed to be due to radiation from, probably plasma radiation, from charged particles trapped in the strong magnetic fields of sun spots.

Sullivan

But what were you making of it at that time?

Wild

Really, very little, from the spectrum. We didn’t really want to speculate on things. We didn’t get a real clue form the spectrum, but there were clues from the fact that they were very strong, correlated with suns spots, especially large sun spots, that’s a result really that Ruby Payne-Scott brought out. So they had to do, certainly seemed to be associated with very strong magnetic fields. But we got nowhere at that time interpreting it.

Sullivan

And did you mention, measure some circular polarization also?

Wild

Yes, although that had been established before.

Sullivan

Also, you mention a minimum in the spectrum at 89 megahertz.

Wild

Yes, that turned out to be a chance thing. The point is that I think we did have a caveat when we described this that we said: the chances of this happening by chance if everything were independent, or the bursts were independent, is something rare indeed, but in actual fact they’re not independent – they’re all taken from about four storms. The number was really four and not several hundred.

Sullivan

I see.

Wild

Small-number statistics. That would have been intensely interesting, but of course, it doesn’t show it. And about this time, I did get very interested, since hydrogen was the main ingredient in the sun’s atmosphere, I got very interested in the spectrum of hydrogen. And when the hydrogen line was discovered, I got an internal report I’d written on the hydrogen spectrum, dusted it, and edited it, and published it in the Astrophysical Journal. It’s one of the earliest papers on this thing.

Sullivan

Right. That was in fact my next question here.

Wild

I was very stupid in that I didn’t buy the possibility of lines, spectral lines in the solar spectrum.

Sullivan

So that was your real motivation?

Wild

That was the real motivation, and ah –

Sullivan

And you did conclude that perhaps this three centimeter line could be visible?

Wild

Yes. Well, it’s still on the cards.

Sullivan

People have tried. Did you every try it that time?

Wild

No.

Sullivan

And, also you recalculated the Einstein A for the 21 centimeter line, which had been incorrect up to that point. I think Purcell –

Wild

I don’t think (he did that, did he?)? No, I think this was, this was Purcell; I don’t think I’ve taken it –

Sullivan

When you say private communication from him?

Wild

Yes. Yes.

Sullivan

Another thing I wanted to ask you about was the recombination lines are dismissed in a —

Wild

One sentence?

Sullivan

Right.

Wild

Yes, well, this is one of my famous sentences I have written. [beginning to laugh]

Sullivan

[laughing] Sorry to bring it up.

Wild

People have reminded me of that many times.

Sullivan

Did you —

Wild

But, I think it’s a perfectly valid statement that they were just undetectable from the kind of equipment that could be dreamt of at that time.

Sullivan

I believe what you said then was that they would be blended together.

Wild

Right, blended together or with, or be distinguishable from the background.

Sullivan

Yes, continuous spectrum. I was just wondering, was that based mainly on the result that van de Hulst had in his famous paper in Dutch, which I guess you had a translation of when you wrote this. Is that true that you had a translation of that?

Wild

No, I think, I don’t know that we ever managed to get a translation of van de Hulst’s paper. It’s a very elusive journal, isn’t it?

Sullivan

Yes, right. So you were —

Wild

My interests were originally in, not the recombination lines, but the fine structure lines. I suppose recombination lines are – no, let’s think, recombination lines are different than main quantum numbers, aren’t they?

Sullivan

Right. Right

Wild

It’s my main interest was the fine structure lines, but that sentence was passed off with a minimum of thought.

Sullivan

Okay. That makes sense if you didn’t see van de Hulst’s paper because he actually did consider recombination lines in that paper and came very close to getting it “right,” but he made a slight mistake in the line broadening calculation and concluded that they would not be detectable.

Wild

I see.

Sullivan

Whereas if he’d done that right, even with the knowledge that was available then, he could have, he might have said at high frequency you could get a few percent line to continuum ratio. But, if you didn’t even see that article, now did you have the translation of the Shklovsky article in ‘48? You refer to that.

Wild

I can’t remember. I can’t remember. I probably did. I probably had it in a –

Sullivan

Now there I can check the date of the translation in the Division here, that might tell you.

Wild

Hmmm. Yes.

Sullivan

So anyway, your main motivation for doing this paper, which is primarily known for its 21- centimeter work, was more to do with solar applications?

Wild

Right, that’s definitely what got me interested to start with. And some of the, I got somewhat interested in lines to use to some instrumental effects in the spectrograph due to mismatches, certain frequencies showed up better than others due to mismatching. Well, until I recognized that they were due to mismatches, I got interested in studying the spectrum, hydrogen spectrum.

Sullivan

You thought they might be real [speaking simultaneously - unclear] I see. That’s interesting – I don’t think you mentioned that in the paper. That was part of why you wrote it?

Wild

I didn’t mention the motivation. I don’t think one usually does.

Sullivan

Well, you’re right, but I would like to put a note in that one should, certainly from a historical point-of-view. It also makes for more interesting reading. But let’s move on. In the volume edited by Kuiper on the sun, you put a chapter in on solar radio techniques, and you also had a review article on radio astronomy as a whole in Advances in Electronics and Electronic Physics. So obviously, your work was becoming known and you were writing review articles. In terms of observational radio astronomy when you wrote that article in 1954, you obviously had to make an assessment of the whole field. Can you put yourself in that time and sort of comment on how you saw the field as a whole?

Wild

Well, I think that by that time, the Radiophysics Laboratory was so imbued with radio astronomy that, and at that time, one tended to keep track of the whole subject which nowadays is very much harder. And one was in touch with, in Australia, with a lot of people working in various different priorities and also again in international meetings, so it was good education on my part to write that article. It sort of made one sit down and read a lot of literature, make an assessment. Well I tried to keep it with a touch of individuality. I even put up a rather crazy type of radio telescope.

Sullivan

What do you mean “put it up?”

Wild

I described an original type of radio telescope, which was a sort of an early version of an aperture synthesis requiring four elements.

Sullivan

I see. I didn’t remember that. Can you just tell me now what —

Wild

Yes, the possibility of photographing radio brightness distribution.

Sullivan

Ah ha.

Wild

So it was a sort of a little bit of a —

Sullivan

So its a bit of a precursor we might say.

Wild

Yes it is. This is this sort of thing. [paper shuffling]

Sullivan

So you worked out the —

Wild

It was really —

Sullivan

The Fourier theory of it.

Wild

Yes, it was really--see the Mills Cross had come along at that time, and this was simulating the Mills Cross with the aid of four elements which were movable. Well, eventually in the final form of aperture synthesis, of course, it’s simpler than all that and you only need two elements. But what I’m saying is that I didn’t want to merely write a review article without a certain amount of original thought.

Sullivan

And you state here “the outstanding technical problem of radio astronomy today is to improve the resolution,”basically.

Wild

Still is.

Sullivan

Clearly that was on your mind. I actually had a note here that I see already you were thinking about image formation.

Wild

Right, right.

Sullivan

So I guess it would be fair to say that this is really the first sort of thoughts that eventually were to lead you to Culgoora, is that correct?

Wild

Yes. And of course, one, we were surrounded by people who were working in this field, Christiansen —

Sullivan

Although, you hadn’t at that stage discovered the rapidly moving sources, I don’t think.

Wild

I think, yes, we would have got the spectrum by then, but not the interferometer.

Sullivan

Yes, but you probably suspected that there might be.

Wild

(?) that was written —

Sullivan

--that was published in 1955, so probably 1954.

Wild

Well, the interferometry came fairly, soon after that, a couple of years or so.

Sullivan

Okay. Let’s move on now to the work with the second spectrograph. Can you tell me–you already mentioned that you decided you needed a properly engineered thing, so to speak–what were the new characteristics you wanted to have in this second spectrograph?

Wild

The most important thing was broad band, much broader band. And we were aiming for something like an (eighth to one band?), I mean three lots of two to one, and this proved to be a very important thing because it immediately paid off. Tipton’s reproducing the harmonics, which we couldn’t have gotten before. The other thing is polarization, more sensitivity, and circular polarization.

Sullivan

Did you want to be able to look at bursts in different single polarizations or were you able to measure the polarization during a burst?

Wild

We tended to, strangely enough, I can’t think how we did it, I think we recorded the two side-by-side. Left and right hand polarization. That was one way of recording. Another was to do it in sort of time sharing. And we also introduced the more convenient type of display of intensity (?) display which was much more automatic, much more economical, but one lost the (?) quantitative intensity detail which was just other another sacrifice, but I don’t think there had been any such detailed observations in intensity to compare with the Penrith ones.

Sullivan

Is that right?

Wild

No doubt nowadays with sophisticated photometers and things, you could probably —

Sullivan

You could do it, but no one (?). Do I remember correctly John Murray telling me that you did have a rough intensity scale that you put on film also?

Wild

Right. Yes, that was just a routine calibration just to give a sort of order of magnitude. But it seemed at that time that one, the early observations showed a lot of interesting things about intensity characteristics, but one was looking for more broader characteristics and didn’t need that detailed intensity profile.

Sullivan

And like you say, it immediately paid off in terms of finding this harmonic structure which you published in a Nature note. That reminded me, I wanted to ask you why did you not send off the note to Nature about the Types I, II, and III? That seemed to be the style around the Laboratory and that certainly was a very interesting result.

Wild

It sort of emerged very gradually, it was quite a low key thing to begin with. And I think it was only at the IAU meeting, I forget when that was 1952, I think.

Sullivan

In Rome?

Wild

In Rome, yes, I think. I wasn’t there, but I think Bolton and Pawsey were there and it caused a great deal of interest and it was only then that one realized that there was something to it.

Sullivan

I see.

Wild

And yet the nearest thing to letters to Nature I think, was that Bracewell was in England at the time and he gave a little account of it at the Astronomical Society, and that did actually appear in the Observatory.

Sullivan

I see.

Wild

Bracewell did a number of things like that.

Sullivan

That’s interesting; so identification of radio sources or some of these other things were looked upon in the group here as worthy of a letter to Nature, but this wasn’t quite at that stage.

Wild

Well, I don’t know but we made up for it later on; we soon got in the habit of writing letters to Nature. The other thing, I suppose, was that one was very dependent on presentations, and at that time, (color?) and it was you had the first (?) you have there, the harmonic one, and you had to go to considerable subtleties and develop a good presentation.

Sullivan

So let’s talk about this paper. When you first saw this [Wild, Muncy, and Rowe (1953) Nature] that must have been quite exciting also.

Wild

Right. Actually, what the history of that is that I think this is the first time the Laboratory ever published a paper in which one of the authors has been a technical assistant and that was Bill Rowe. And it’s since become a much more regular thing. But the reason was that he through his own initiative, he went down and recorded, I think it was a Sunday or something like that, and while he was there, he switched the equipment on and then went into (Wollangong?) to do some shopping, and while he was in (Wollangong?) this occurred. And never was a place more deserving to have his name on paper. And he described it to me at the time and we could hardly wait for, I think we did our own processing on the spot, I’m not sure. But I remember taking the film home; it was a very washed out sort of film—a very expanded time scale. But it was quite clear that there were two very distinct frequencies. And one had no idea what the relationship was between the two frequencies. The excitement came when the two-to-one figure came, and I remember that I got it back at home in Sydney and the (?) measurement and it kept on coming up two-to-one, that’s (?).

Sullivan

But what about when closer inspection showed that it was really 1.95?

Wild

Well, I suppose, it always has the immediate reaction that one is disappointed that it’s not something nice and simple. But when once you’re convinced that it still has something to do to two-to-one, it becomes much more interesting. And that’s a very common thing, I think. You hope things will be simple and straightforward, but it’s usually more interesting if it’s not.

Sullivan

Right, but it is less information content.

Wild

Right.

Sullivan

And so did it take you long to come up with the reasoning that you did as to why it was not exactly two-to-one?

Wild

I think it was a fairly immediate conclusion. At first almost as a joke, and then realized that there’s perhaps not much else it could be.

Sullivan

I’m just noticing here also that you only had this one case when you sent in the letter to Nature. And then you had a note added in proof about a second one.

Wild

Right. I think the thing is that it’s one case which has so much information, that you only need one case in a case like this.

Sullivan

You had no fear about a birdie in your system?

Wild

No fear whatsoever. A lot of my colleagues, including Bernie Mills I think, were very suspicious that it had something to do with an instrumental effect. But, it had one very great safeguard in that the two harmonics most of the time were recorded on two entirely different signals. And so because of that—

Sullivan

Yes, yes, that’s definitely (?).

Wild

(?) two-to-one.

Sullivan

And the fact that they were not exactly two-to-one was again (?).

Wild

Yes, even more so.

Sullivan

Argued against that.

Wild

Yes, it still remains one of the, one couldn’t ask for a better example to come along first. Many, many have come along since, much less impressive.

Sullivan

For my information, in our current understanding is the explanation of this harmonics, and the fact that it’s not exactly two-to-one, is that still the basic explanation?

Wild

Yes, I think there’s very little—that was extremely important at the time to establish. To make a case for the fact that there were harmonics. But I think very little work has been done on that since; once established, it’s just become accepted now.

Sullivan

Well, let’s see. Let’s move on to, oh this paper I wanted to ask you if it’s referring to you, and article with Krook and it was just P. Wild, but it was you?

Wild

Yes, yes.

Sullivan

You, at this time, you apparently were in America, in 1956 at an AAS meeting, and was also a thing in the Sky and Telescope about it. And here you are talking about shock waves in Type II and Type III bursts. So can —

Wild

I’d completely forgotten that paper.

Sullivan

It was just an abstract, so it never became —

End Tape 90A

Begin Tape 90B

Sullivan

This is continuing with Paul Wild on 3rd March 1978. So how did this interpretation of shock waves come about?

Wild

Max Krook was a plasma physicist.

Sullivan

At which institute?

Wild

This was at Harvard. And I was at Harvard at this time with Allen Maxwell most of the time, but Max Krook had the room down the corridor. He was very interested in these phenomena. He didn’t believe our story about Type III bursts being very fast particles; he was convinced that they were some kind of shock wave or shock phenomena, or wave phenomena. We talked a great deal about the slow and the fast types and we must have written a joint paper together. But I can’t remember the details.

Sullivan

Well, what I have in the abstract is the Type II were shock waves in the electron ion gas and the Type III were shocks in the electron gas.

Wild

Yes, well that’s – the latter at least is pure Krook.[laughter]

Sullivan

And the first is Wild, right?

Wild

I’m not sure that I understood the whole thing or his theory, but he was a very nice chap and we got along together very well.

Sullivan

Anyway, this explanation for this Type II burst is still in currency?

Wild

Yes, I think I came out with it most strongly I think, in a definitive way in, I think it must have been, 1957. Identifying Type II as a shock wave.

Sullivan

And was that a joint paper?

Wild

That was at a, yet another IAU meeting.

Sullivan

You mean the Paris symposium? That was 1958. The Dublin meeting perhaps?

Wild

What was at the Dublin meeting? It must have been the Dublin meeting.

Sullivan

The reference I have is a joint discussion on solar flares where you talk about Type III and then Type II, and then you get prolonged storminess.

.

Wild

Yes, it was that Dublin meeting, then. We can check that later on.

Sullivan

So you were convinced even before going to the US that there were shock waves involved?

Wild

Yes. It was stimulated by the, well the observation of the harmonics. Basically, a non-linear phenomenon in shock waves basically known. There was an element of speculation in it. It was established by suggestion rather than very firm criteria.

Sullivan

Well, since you brought up the Dublin meeting, and I think you also went to the Jodrell Bank symposium, didn’t you?

Wild

Right.

Sullivan

Any recollection of that meeting?

Wild

Yes.

Sullivan

Can you tell me of any recollections you have of your work and how it was received and what you learned about what else was going on?

Wild

I think the highlight for me was the paper that you’re reading now, was giving a presentation to, what do they call it, a joint discussion. Where I suppose it was the first time I’d given a sort of major contribution to, before an international audience. I suppose I was very nervous before I started, but then I got confidence and it was very well-received. And there was an enormous barrage of questions at the end.

Sullivan

Oh yes, in fact, they are recorded here. Jennison asked, “Have other harmonics been observed?” and you say, “Regret, no.”

Wild

I think you have to make an allowance for the reporter, you see. And I think Richard Twiss, I know Richard Twiss came (?). That was the first time I’d met him. But that, I think, was the highlight for me. The Jodrell Bank symposium was very interesting, too.

Sullivan

What do you remember from that?

Wild

I thought it was, I think the thing I remember mostly was Martin Ryle presenting his source count data, and Joe Pawsey doing a magnificent rebuttal in a way, very modestly, on the basis of Mill’s preliminary results. And Pawsey’s performance reminded me of Marc Antony’s speech. “Brutus is an honorable man, “in reference, to Martin Ryle.

Sullivan

Right.

Wild

But he absolutely won the day, and I’ve never seen a better performance from Pawsey. However, that was the (?).

Sullivan

Going back to the Dublin joint discussion, you established a rather nice correlation which is shown in Fig. 5 in this paper, where Type III burst velocities correspond nicely to the implied cosmic ray velocities and the Type II correspond to magnetic storms. This is the first time that anything had been done like this I guess.

Wild

Right. Now the cosmic rays, I can’t remember, that’s right. That turned out, I think, to be wrong in the sense that cosmic rays from the sun which arrived at the order of half an hour or twenty minutes or something like that. I think now those long time delays are not due to relatively slow velocities (or the observed velocity of light?) but much more to (?) differences; and no one there believes, I think that —

Sullivan

You mean going as not directly —

Wild

Yes, or going in spirals, this sort of thing. But that made a very nice story at the time, but the correlation has been (?).

Sullivan

But the other one is a valid inference between Type II burst and the magnetic storms?

Wild

Yes, that’s fair to say.

Sullivan

Well now another point is that you say that there was a great deal of interest in this paper. This was 1955 and yet your results had been around for four or five years basically. Was this simply because they weren’t generally known?

Wild

No, there were lots of rather new things, but really this is based on the harmonic which is fairly, what was that?

Sullivan

That was 1953 so that was two years old.

Wild

1953. Then the fact that the correlation between Type III bursts and flares, which was – have you got that there? That was a letter to Nature - that was Wild, Murray, Ryle, Robertson, and Murray.

Sullivan

1954 in Nature.

Wild

Yes, that’s right.

Sullivan

Yes. Type III spectra implied velocities of about hundred thousand kilometers a second.

Wild

Right. So combine those things and I suppose it was reviewing stuff which had been published a year or so. But it’s just a question of having an open discussion.

Sullivan

Yes, but it seems to me that it might well be that many of the solar physicists in related fields just didn’t know about this, even though it had been around for a couple of years.

Wild

That’s quite right, too. At that time, I don’t suppose the optical people took very much notice of the writing. They applied to all fields.

Sullivan

I don’t think they were reading the Australian Journal of Scientific Research as much as they were reading Ap J.

Wild

No, that’s right. So it was quite a good thing in a way that radio astronomy had a low profile in astronomy from the beginning.

Sullivan

Why was that?

Wild

Well, it I suppose, it allowed the truth to firm up before it was under too much scrutiny.

Sullivan

If you mean that radio astronomers at that time would learn about precession and things like this, I’ve heard some interesting stories about that in the late forties. Okay, let’s move on. You have a paper with Wild, Murray, and Rowe in the Australian Journal of Physics; that was really a follow-up of this —

Wild

The whole detailed (?) of the Nature.

Sullivan

Yes. You’re talking about longitudinal oscillations excited by fast particle streams. Where was the plasma physics coming from? Was that, once again, just a matter of getting the right book and – ?

Wild

No, I think that in this lab, Westfold and Smerd were our theoretical people who used to keep us on the ball with plasma physics. And we picked up what plasma physics we could with their assistance.

Sullivan

I also noticed in that summer of 1955 you went to a discussion on solar flares at University College in London, and there was another London meeting on solar eclipses in the ionosphere.

Wild

Yes, I think that was just doing the rounds.

Sullivan

These were not particularly oriented towards radio astronomy?

Wild

Not particularly, but they were – this is the paper that came out of that.

Sullivan

Right, on the ionosphere.

Wild

Right. There was obviously an interest in this bit of a rehash of the –

Sullivan

Right. Same figures as the Jodrell paper.

Wild

And this is not unknown when one’s –

Sullivan

Oh, sure. So there was nothing substantially different?

Wild

No. It was purely a rehash.

Sullivan

What else do we have? Let’s see, you alluded earlier to getting tired of not finding any flares out at Dapto and then beginning to look at Cygnus A fluctuations. Can you tell me about what you found from those observations?

Wild

Well, we thought that while activity was so low it might be interesting to look for other applications of that equipment. We did a few simple calculations to see what sort of an aerial one would need and indeed, one could do a very good job of the horizontal rhombic, a very large one. So all that needed was supports and some posts and some wire, which we rigged up fairly, quickly. Quite fixed, it was pointing north; Cygnus comes up north of the horizon. And switched it on the first evening, and it was tremendously interesting spectacle of what looked like a whole series of Type III bursts. And I can remember ringing up Joe Pawsey and telling him – they were all going from high to low frequencies, and he was very, very intrigued. He said, “Perhaps the original explanation of those scintillations was right after all, the fluctuations are right.” But they were in fact, bursts —

Sullivan

In the source? Did you really entertain that idea for a while?

Wild

We didn’t know what was going on. That first night, you couldn’t tell until you calibrated everything and saw whether it went below the line as it were. Dips were below the line and the average sort of evened out. Well, after that very high beginning, we then got involved in a sort of taxonomic study almost of the different kinds of fluctuations which produced some very nice optical effects, interference effects. That kept us amused for I’ve forgotten how long it was, perhaps a year almost. And we got involved in all sorts of correlations and somehow scintillations wore a bit thin after a while, after writing one major and one minor paper, Jim Roberts and I. And we were rather glad eventually to get back to the sun which is a more scientifically interesting subject.

Sullivan

Well, I was going to ask you something related to that, namely, here you spent almost a decade working on the sun and yet you’re quite willing to just go off and work on the ionosphere for a year because the equipment is there or something.

Wild

Yes, quite right. It was just because of boredom with the sun. I think it’s a good thing not to get too stuck in one thing for too long. That’s why the next phase after that, of course, was when we went into interferometry.

Sullivan

But still the sun, but a rather different instrument. Let’s see if we find anything else before then. Well, there is this sideline here where you and John Bolton proposed a 12 cm. Zeeman Splitting in 1957. How did that come about?

Wild

Well, I was doing my 1956 visit to the States; it began in 1955-56 with Cambridge and then Dublin. I was sort of on my way home and my last port of call was in Pasadena with John Bolton. And I had a visit for just a few days there. Really, I can remember it was the morning after a very memorable party that was held with all sorts of very distinguished people, but only (?). We went to Mt. Wilson and Babcock was on measuring magnetic —

Sullivan

Magnetogram (?)

Wild

And it emerged out of that, seeing that, and I suggested to John, why couldn’t one look for Zeeman effects and spectral lines doing this, and I started sort of thinking about line widths and things and whether it was feasible. John’s contribution was really to say, “Ah, what you want is an absorption line because it’s much narrower.”

Sullivan

And the switching idea?

Wild

Right, and the switching, yes. That was part of it; that was really Babcock. And the following day I wrote that short note and put the idea on paper – never has such as short article been responsible for wasting so much time by so many people, but —

Sullivan

Well, eventually not wasted.

Wild

No, not eventually, but it did seem at one stage as though people were spending years and years of Ph.D. time not getting anywhere.

Sullivan

Once again, neither you nor Bolton tried this yourself?

Wild

I think what we were saying was that when more sophisticated instrumentation comes into play, as it were, larger dishes and so on, and at Jodrell Bank, I think, at that time (main effect?). It was very much as passing thing that just arose out of a few days visit.

Sullivan

Now I understand, it obviously looks strange amongst all these other papers here. Now, there’s a paper here with Steve Smerd in 1957 in Phil Mag. where you talk about strip scan solar observations and how to interpret them.

Wild

That was written by Steve in my absence, and I tried very hard to get out of the authorship, but I think it was (?). However, I did give a, I thought it was much too complicated the way he presented it, but I did give a very simple version of it in another paper that was probably same IAU, maybe —

Sullivan

Jodrell Bank Symposium?

Wild

Jodrell Bank Symposium – that was a very simple version of it. Steve was working on this problem, and I just came up with an idea which helped simplify (?).

Sullivan

Okay. Let’s go back to the States again where you went to another AAS meeting and talked about the association with Zerin, erupted prominences and 167 megahertz bursts.

Wild

Yes, well, while I was in the States, I spent about 3 months at High Altitude Observatory in the wooden huts of the time. Which is quite — . Sidney Chapman was there most of the time; Walter (Robertston?) was there, too. And Hal Zerin and I did a comparison, I was very much interested in the radio side of things and Boulder had a very large collection of optical records which they didn’t do anything with, and also, sorry, of radio records which they didn’t do anything with, and also miles and miles of prominence film. So, I suggested that we get together and look for correlations. The paper which eventually appeared, this one —

Sullivan

In the Australian Journal of Physics.

Wild

Yes, that was the paper.

Sullivan

Right. But now perhaps the interesting thing that came out of this in my view is that you found that when they got to the center of the disc that you got the noise tones. Was this the first indication of some directionality in the radio bursts or did you have some earlier?

Wild

I think there must have been indications of this from the early days, even very early papers by Ruby Payne-Scott. And even before that, even Hey might have –

Sullivan

Hmm. I don’t remember that, but it could well be.

Wild

The directivity of — well, it probably wasn’t Hey because he didn’t recognize the phenomenon of (?) storms. But I think the concept of directivity probably was earlier than that, but this was tying it up with the —

Sullivan

Tell me about the rest of your stay in the U.S., in particular, which radio places you visited and what your assessment was of what they were doing.

Wild

I can’t remember what places I went to, but the main places were Harvard for about three months, and then Boulder for about the same time, and then Michigan, Fred Haddock, also for about three months, and then to the west and spent some time, again, with Maxwell just before he went on the air at Ft. Davis. And it’s a rather a (sore ?) to say, but it was there I actually (?) first U-burst, which was (?) published.

Sullivan

I’m sorry, I don’t quite get what you’re saying.

Wild

A U-burst, Type III which —

Sullivan

Right. What did you say about it?

Wild

Well, this was really the first Harvard discovery, the U-burst, but we got one isolated at some point, but they got and recorded (a vast number?).

Sullivan

What was the ability that they had that enabled them to see them easier?

Wild

I’m not sure. I think it was probably just a matter of a pretty small sample of activity that we’d recorded up to that time.

Sullivan

Was it detected with an 85 foot dish?

Wild

Well, they did have an 85 foot dish. I don’t know, but they were a very common phenomena, you know.

Sullivan

But now were you more or less the technical advisor for the spectrograph?

Wild

It was Donald Menzel, really. Or was it Menzel or no, maybe it was Leo Goldberg, Menzel and Goldberg between them. No, it was Donald Menzel; Leo had gotten along to Michigan. Yes, I suppose at that time I was – they wanted to start off in this field, and I was the only one in the group that had done it before. So it was a very instructive time.

Sullivan

In the Harvard spectrograph, what were the main differences from your own?

Wild

Well, of course, one of the main differences is that they did it in the American style, which is to subcontract. I think it was (?). And so everything was very professionally done, factory produced and all this sort of thing. Yes, this sort of method of budgeting is entirely different than ours. But probably quite sensible when you consider (?) and everything. I don’t think I made a very big contribution or anything really more than could be cut out of the papers. Bits here and there. Although I think there may have been a few — Yes, there were a number of things where they were quite clearly doing the wrong thing. But they could have been cleared up in a couple of days, so my main interest at Harvard was probably talking with all the astronomers and graduate students.

Sullivan

Such as Menzel?

Wild

Well, there were a whole lot of graduate students. Donald Menzel himself I saw quite a bit of because for a while I actually stayed with him in his house.

Sullivan

So, did you learn anything in terms of equipment in your stay in the U.S. or was it mainly only some astrophysics that you were learning?

Wild

Well, I don’t think I did very much because I wasn’t, one was so remote from the technical scene, which was really in the airborne instrumental labs. And certainly, I did go around the labs, but of course, you don’t learn very much.

Sullivan

Right. I mean when you visited Michigan or Caltech.

Wild

Well, I think that probably I encountered some people that were, was it Henry Jasik, the antenna king?

Sullivan

Yes.

Wild

I think so. And then there were a whole lot of people at Michigan involved, was it then or later? In optical transforms and things like that, which was interesting to me, too.

Sullivan

Once again, this is leading on to Culgoora and (?).

Wild

Yes, but on the whole, my main interest in instrumentation is in systems as a whole, I think, and I’ve never been, I’ve never done much nuts and bolts engineering with my own hands. I’m not very interested in systems.

Sullivan

Okay. Let’s move on to the next major instrument you were involved with which was the swept frequency interferometer I believe. You operated the Dapto Station until the early sixties, I guess.

Wild

Yes.

Sullivan

But at what stage did you feel the need for something else?

Wild

It was stimulated by, oh, you mean the swept frequency interferometer?

Sullivan

Yes.

Wild

Well, I think it was essential to keep things moving. We scooped the cream out of the pure spectrum by itself there were some very important (?) hypothesis was a hypothesis and nothing more. It needed really confirmation. And a few quick sums show that you could put together an interferometer without too much effort which could answer a lot of these questions. In actual fact, it was quite a lot of effort.

Sullivan

What period was it developed over?

Wild

I suppose it started when I got back from the States.

Sullivan

1956?

Wild

We had started a bit of this before with scintillation work. We had some interferometric measurements for the Cygnus scintillation work, but the whole thing had to be completely changed. Servicing. Needed delay lines and all sorts of things.

Sullivan

Yes.

Wild

I don’t know whether you’ve had a look at the paper on the interferometer.

Sullivan

Not the paper itself, but the abstract.

Wild

It was quite an extraordinary (Keith Robinson?) for while it was operating there were tremendous noises going on all the time; windows going in and out and moving parts, (?) recorder.

Sullivan

I guess Kevin Sheridan was working with you.

Wild

Yes, Kevin was, well this was the time Kevin was more or less removed forcibly, against his will, to do it.

Sullivan

On this?

Wild

On this.

Sullivan

What was he doing before?

Wild

He was the Bernie Mills, but Pawsey actually, while I was away, just before I returned, Pawsey said that Dapto needed reinforcing technically, which it certainly did at that time, since John Murray. And Kevin, very much against his will, was transferred.

Sullivan

Well, if I remember correctly now, Murray was taken off to go to the hydrogen line receiver because that needed reinforcing.

Wild

Right. Right. And that left us with a void; we had Jim Roberts and myself, who were both physicists. When I went away and Max Komesaroff who was not at all a practical man, but very much the dreamer and philosopher; so we had a very almost zero technical competence. Then Bill Trent who was the technical officer added very solid support on the technical line, but not in the way of engineering. And Kevin was a tremendous boon. And as I was saying, it was against his will to begin with, but it took about six months and then Kevin, you can ask him yourself, but I think he was pleased with it then.

Sullivan

In that it got him into solar work?

Wild

Well, yes, and I think in a working environment which was probably much better than his previous one.

Sullivan

It seems to me that well, I get the picture that Pawsey is sort of looking at all these small groups, I guess there were five or six of them at least, and sort of moving the pieces around.

Wild

Yes, I think this is a good example. I suppose that (?) that maybe we weren’t aware of, but I suppose that’s what happens within the CSIRO Division. The way they work is to let things run and then every now and again review things and see how best to use the resources.

Sullivan

And you get reassigned and that’s it?

Wild

Well, I think it was, Kevin’s reassignment was quite, almost against his will, it was quite an unusual one. Usually you talk someone into it.

Sullivan

I guess that’s the problem of management. Okay. So now with this interferometer, what were you able to establish? What were the main results that came from that? I see two papers here with Sheridan and Trent, and Sheridan and Neylan.

Wild

Right. The, I can remember that when I came back from America I found Dapto in a state of rather low morale. And I got working hard on the interferometer, and there was some skepticism as to whether it would ever work.

Sullivan

Why was that?

Wild

Well, all sorts of things. Like would open wire transmission lines be suitable for linking two elements or would there be too much leakage or too much continuation. It was also very complicated. Keith Robinson talking about lots of parts moving and all sorts of things that can go wrong. I can remember that Jim Roberts left us about that time.

Sullivan

Went to Caltech?

Wild

No, at that time I think he’d left Dapto to go and work out some of the solar results. And then he was going abroad I think to some IAU meeting.

Sullivan

Paris Symposium?

Wild

Yes, that’s right.

Sullivan

Did you go to that meeting?

Wild

No, I didn’t. I stayed behind to try and get some results to present at the symposium. And Jim left, I think it was about five weeks before the symposium because he was going to Russia to a Moscow meeting. At the time he left, we had nothing to show whatsoever. We had no results from the interferometer. During the next five weeks, we almost got the picture clear but it was the first five weeks of operation, and we were able to confirm the plasma hypothesis and get a number of interesting results about Type IIs and Type IVs, and that was quite a useful, that was quite a significant contribution, I think.

Sullivan

What was the key to this confirmation?

Wild

[pages turning] Let me see. Can we switch this off a moment?

Sullivan

What was this Wild, Sheridan, and Neylan paper that you say was a key?

Wild

Well, the key diagram in that really was again, a colored one, in which it was showed about a dozen or more examples of limb flares. Once the position of the limb flare was shown and the level at which the radio emission, four or five different frequencies, as measured by the interferometer was shown in four or five different colors. And every case the Type III bursts coming from (?). And in every case, it was regular sequence, the low frequency being farther out and the high frequency being close in. And it was quite a, it had to be very carefully interpreted, the results, because we had to make allowance for ionospheric refraction which was quite tricky, but —

Sullivan

And different at the different frequencies?

Wild

Right. And so one also had to study what happened during the continuum storm, and you could see the way the different frequencies at the time moved about. On some days there was an enormous swing, and obviously results were meaningless, and on other days, it was very well (?). You had to sort all those things out. But what emerged quite convincingly was the confirmation of the plasma hypothesis.

Sullivan

And these very high speeds?

Wild

Right.

Sullivan

You said that at first, you referred to 55, that there was a lot of disbelief about these five speeds.

Wild

Right.

Sullivan

Had they been accepted by this time?

Wild

Well, as a result of this, I think this had to come first. Of course, one could still argue that it might be a particle, that it might be a wave rather than a particle. And the next step was really taken by one of my colleagues, quite a junior one at that time, Ron Stewart, who did a systematic investigation of the, not at any speeds, but accelerations of Type III bursts and came to the conclusion that on the whole, speed tended to be constant throughout, so that the lower one was dealing with Newton’s first law of motion.

Sullivan

As opposed to electro-magnetic phenomenon?

Wild

Right. Well, plasma phenomenon, a plasma wave was never, you couldn’t imagine a plasma wave remaining constant velocity over the enormous range —

Sullivan

Andy density, yes.

Wild

And I show that out of this Type III phenomenon, it’s one of the most puzzling things in plasma physics, it’s a problem of extreme interest now, I think in it’s own sake, how a bunch of particles manages to keep emitting plasma oscillations of plasma waves, manages to maintain its identity all the way.

Sullivan

You mean coherent (?)

Wild

Right. All the way from lower solar atmosphere, and now we know right out of space because of the Type III bursts we’ve picked up, close to the earth.

Sullivan

That’s still a puzzle?

Wild

Yes, and a plasma theory of very sophisticated puzzle that doesn’t bother most astrophysicists.

Sullivan

I wonder if you know enough to turn your back on it. So that was perhaps the primary result that came from the swept frequency interferometer, would you say?

Wild

Yes.

Sullivan

How long did that instrument operate?

Wild

Not so very long. I think we did the right thing when we got our results and then closed it down.

Sullivan

And when was this closing down?

Wild

I can’t remember if it was eighteen months or —

Sullivan

Something like that, yes.

Wild

Yes. Then we operated, then we got increasingly, well, what it led to is the (?) radio heliograph. I suppose I started thinking about a radio heliograph while I was still in the States. It was the obvious next step, trying to get radio pictures of the sun.

Sullivan

And so, in fact, from 1959 or ’60 when the radio heliograph went into operation, which was 1967?

Wild

Between about 1960 and 1967, my attention was almost entirely devoted to a little bit of dabbling in interesting records that came along, but mostly thinking about that heliograph.

Sullivan

So can you just outline for me what the sequence of critical events in the design and construction of the radio heliograph were? I guess going right back to the States?

Wild

Well, I suppose the —

End Tape 90B

Click start to listen to the audio for tape 91A of the 1978 interview.